Role of WRB protein in cardiac function

Abstract

The mammalian TRC40 system is a conserved pathway responsible for the post-translational targeting of tail-anchored proteins, which are characterized by a single transmembrane domain at the C-terminus and an N-terminus that faces the cytosol. The cytosolic ATPase TRC40, Get3 in yeast, binds newly synthesized TA proteins and targets them to the ER where they are inserted via a membrane receptor formed by WRB and CAML, functionally equivalent to yeast Get1 and Get2. This heteromultimeric membrane protein complex works as a docking site for TRC40 and "insertase" for TA proteins. Although several molecular aspects of the pathway have been elucidated in recent years, it is poorly understood how the pathway is integrated into the cellular proteostasis network in vivo. In order to gain insight into this question, the fate of several TA proteins (Sec61β, syntaxins 5, 6 and 8 and emerin) was evaluated in a heart-specific, inducible knockout of WRB mouse model. Our analysis showed that endogenous syntaxin 5 and emerin are reduced upon WRB depletion. On the one hand, we observed that syntaxin 5 is degraded by autophagy upon disruption of the TRC40 pathway, constituting a novel mechanism for the clearance of TA proteins. On the other hand, our results confirm that emerin, a clinically relevant TA protein of the nuclear envelope, depends on the TRC40 pathway for its insertion into the ER and targeting to its final destination. Our results suggest the TRC40 pathway does not only contribute to insertion fidelity of its clients but also to their overall stability.